It is well known that Multimedia Broadcast/Multicast Service (MBMS) channels require large amounts of power in order to satisfy the Quality of Service (QoS) requirements with adequate coverage. This power requirement can be reduced by using one or more of several known techniques such as power control and diversity. Diversity transmission can be in the form of retransmissions, which provides time diversity, or in the form of spatial diversity such as macro-diversity. Macro-diversity inherently exists in cellular systems when the same MBMS information stream is provided in adjacent cells. However, in order to take advantage of this form of diversity, a mechanism is needed to combine the signals from the diverse transmissions. Prior-art proposals for maximum-ratio combining (MRC) (such as has been done in the well-known rake receiver) and selection combining (SC) exist. The MRC technique is known to provide the best performance but severely constrains the relative transmission delays between the cells. Selection combining, on the other hand, relaxes the delay constraint at the expense of a performance loss (average transmitter power increase on the order of 2 dB for typical conditions).
Thus, what is needed are apparatus and methods for adapting a diversity transmission mode in a wireless communication system. These preferably will match the performance of MRC when possible, and will trade delay constraints for performance gain.